Desktop telecommunication systems are known wherein a computer workstation is provided with a communication interface for connecting with a telephone line so that a local user can converse and/or exchange data with a remote user at a similarly-equipped computer workstation. Typically, the communication interface includes a pair of jacks for connecting the speaker and the microphone of a telephone handset with a personal computer to allow "hands-free" voice communication. Additionally, such communication interfaces allow interactive voice control of the computer workstation, a remote computer or other voice-response systems; desktop video conferencing; screen sharing; audio graphics; and computer-controlled telephony. Examples of such communication interfaces include the PROSHARE audio card, manufactured by the Intel Corporation of Chandler, Ariz., and the VC8000 audio adapter manufactured by British Telecom.
Telephone headsets are preferable over handsets in desktop telecommunication systems because the users of such systems may be required to operate a keyboard or a mouse during a telephone discussion. Such headsets are disliked by many users for a number of reasons. In video conferencing systems, for example, some users are not pleased with their appearance when wearing a headset. Telephone headsets can be uncomfortable, particularly for extended periods of time. Telephone headsets also prevent multiple users at a single site from participating in a conversation, and the headset user is effectively tethered to the workstation. Additionally, the sequential use of a single headset by several users is unhygienic.
Accordingly, it is desirable to provide a speakerphone device adapted for connection with a desktop telecommunication system. The particular demands of desktop telecommunication systems have, heretofore, militated against the use of speakerphone devices. For example, it is important for such a device to be of a more compact size than a traditional speakerphone, so that the device does not significantly contribute to the clutter of various computer workstation equipment, such as a computer, keyboard, mouse, video camera, and the like. However, as the size of a speakerphone is reduced, various problems in speakerphone operation have been encountered. For example, there is the tendency toward acoustic coupling, or feedback, between the microphone and the speaker as they are moved closer together. Such acoustic coupling can result from airborne audio paths between the speaker and the microphone. Such airborne paths include acoustic paths that can be internal and external to the speakerphone.
Additional acoustic coupling problems can result from audio vibrations propagated within the structural components of the speakerphone from the speaker to the microphone. The effects of such coupling can be perceived by the user as howling, squealing, or echo, all of which can adversely affect the speakerphone in providing intelligible conversation. The degree of acoustic coupling within a speakerphone serves as a practical limit of the amount of gain, and hence the volume, that can be provided to the speaker.
One way to attempt to eliminate acoustic coupling in a speakerphone is to selectively activate the microphone and the speaker, depending upon the relative amplitudes of the locally-generated and remotely-generated audio signals. Voice switching circuits for performing such selective activation have not been entirely satisfactory, because they produce such effects as clipping softly-spoken syllables and have limited the participants to speak in sequences.
In order to provide for full-duplex conversation, high quality speakerphones employ adaptive echo cancellation circuitry which predicts and synthesizes an expected feedback signal, and then subtracts the expected feedback signal from the outbound microphone signal. Although echo cancellation provides significant advantages relative to voice switching, it is not entirely effective to reduce airborne and structural feedback within a speakerphone device of desired compact size for computer workstation-based telecommunications. Therefore, it would be desirable to minimize, via acoustical techniques, the degree of acoustical coupling within a speakerphone device, which facilitates intelligible conversation. It would further be desirable to combine such acoustical coupling reduction with echo cancellation in order to provide a compact speakerphone device. Such a compact speakerphone device would also be desirable for other applications requiring hands-free voice communication, in addition to having particular utility in workstation-based telephony.